We are studying the incidence and specificity of placental proteins (chorionic gonadotropin and its free alpha and beta subunit, placental lactogen, and placental alkaline phosphatase) as cancer markers. These proteins appear to distinguish cancers from benign tumors and correlate with the response to therapy. Various permanant cell lines have been established to study the regulation of placental protein synthesis in vitro and to characterize the properties of these materials. We have succeeded in translating placental messenger RNA in a cell-free wheat germ system and in characterizing the various products by immunologic, physicochemical, and biologic methods.